Modulated power supply for reduced parasitic capacitance

ABSTRACT

An input device comprising a display device having an integrated capacitive sensing device. The input device includes a plurality of sensor electrodes a plurality of display electrodes, a modulated power supply configured to provide a modulated reference signal, and a processing system. The processing system includes a sensor module configured to drive a plurality of sensor electrodes with a modulated capacitive sensing signal that is based on the modulated reference signal for capacitive sensing during a first time period. The processing system also includes a display driver module configured to drive a plurality of display electrodes of a display device with modulated signals based on the modulated reference signal during the first time period. The modulated signals cause voltage between the plurality of display electrodes and the plurality of sensor electrodes to remain substantially constant.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/278,893, which is a continuation-in-part of U.S. patent applicationSer. No. 14/042,694 filed Sep. 30, 2013, both of which are incorporatedby reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to a method andapparatus for touch sensing, and more specifically, a capacitive touchsensing device having a modulated power supply.

2. Description of the Related Art

Input devices including proximity sensor devices (also commonly calledtouchpads or touch sensor devices) are widely used in a variety ofelectronic systems. A proximity sensor device typically includes asensing region, often demarked by a surface, in which the proximitysensor device determines the presence, location and/or motion of one ormore input objects. Proximity sensor devices may be used to provideinterfaces for the electronic system. For example, proximity sensordevices are often used as input devices for larger computing systems(such as opaque touchpads integrated in, or peripheral to, notebook ordesktop computers). Proximity sensor devices are also often used insmaller computing systems (such as touch screens integrated in cellularphones).

Many proximity sensor devices utilize an array of sensor electrodes tomeasure a change in capacitance indicative of the presence of an inputobject, such as a finger or stylus, proximate the sensor electrode. Manyschemes are possible for capacitive touch sensing. In one scheme,“matrix sensing,” sensor electrodes arranged in a grid or “matrix” aredriven to generate a capacitive image. The sensor electrodes may bedriven in an absolute capacitance mode, in which the sensor electrodesare driven with a signal to determine the degree of capacitive couplingbetween the sensor electrodes and an input object, if present.

Sensor electrodes driven in absolute sensing mode may experience effectsrelated to parasitic capacitances between the sensor electrodes andconductive objects other than an input object. More specifically,conductive objects that are associated with the input device contributeto the capacitance sensed by a sensor electrode driven for capacitivesensing. The existence of parasitic capacitance reduces the ability todetect the presence of an input object. This issue is more acute in“in-cell” display embodiments, in which the sensing electrode is a partof a display pixel cell, and therefore the sensing electrode is veryclose to several conductive elements, such as the pixel electrode of adisplay cell, and the terminals of a pixel transistor, among others.

Thus, there is a need for an improved proximity sensor device.

SUMMARY OF THE INVENTION

Embodiments described herein include an input device comprising adisplay device having an integrated capacitive sensing device, a methodfor capacitive sensing, and a processing system for a display devicecomprising an integrated input sensing device.

In one embodiment, a processing system is provided. The processingsystem includes sensor circuitry configured to drive a first sensorelectrode of a plurality of sensor electrodes with a modulatedcapacitive sensing signal that is based on a modulated reference signalfor capacitive sensing during a first time period; wherein during thefirst time period a plurality of display electrodes of a display deviceis driven with modulated signals based on the modulated referencesignal.

In another embodiment, an input device is provided. The input deviceincludes a plurality of sensor electrodes, a plurality of displayelectrodes, a modulated power supply, and a processing system. Themodulated power supply is configured to provide a modulated referencesignal. The processing system is configured to drive a plurality ofsensor electrodes with modulated capacitive sensing signals that arebased on the modulated reference signal for capacitive sensing during afirst time period and to drive a plurality of display electrodes of adisplay device with modulated signals based on the modulated referencesignal during the first time period.

In another embodiment, a method is provided. The method includes drivinga first sensor electrode of a plurality of sensor electrodes with amodulated capacitive sensing signal that is based on a modulatedreference signal for capacitive sensing during a first time period.During the first time period a plurality of display electrodes of adisplay device is driven with modulated signals based on the modulatedreference signal. The plurality of display electrodes and the pluralityof sensor electrodes have a substantially constant voltage differentialduring the first time period.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic block diagram of an input device.

FIG. 2A illustrates a simplified exemplary array of sensor elements thatmay be used in the input device of FIG. 1.

FIG. 2B is an isometric schematic view of a display device integratedwith an input device, illustrating parasitic capacitance.

FIG. 3 is a cross-sectional partial schematic view of a liquid crystaldisplay cell.

FIG. 4A illustrates a graph depicting operation of a conventional inputdevice with touch sensing and pixel updating occurring simultaneouslywithout a modulated power supply.

FIG. 4B illustrates a graph depicting operation of an input device withtouch sensing and pixel updating occurring simultaneously, utilizing amodulated power supply.

FIG. 5A illustrates a schematic diagram of a display device integratedwith an input device.

FIG. 5B illustrates an example circuit for providing a modulated voltageto a pixel transistor gate.

FIG. 6 illustrates an example circuit for driving a sensor electrode forcapacitive touch sensing.

FIG. 7A is a close-up top-down view of a portion of display panel.

FIG. 7B is a close-up top-down view of a portion of display panel.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation. The drawings referred to here should not beunderstood as being drawn to scale unless specifically noted. Also, thedrawings are often simplified and details or components omitted forclarity of presentation and explanation. The drawings and discussionserve to explain principles discussed below, where like designationsdenote like elements.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

Various embodiments of the present technology provide input devices andmethods for reducing parasitic capacitance in a capacitive sensing inputdevice. Particularly, embodiments described herein advantageouslyutilize a modulated power supply to modulate signals within an inputdevice to reduce the parasitic capacitances experienced by sensorelectrodes in the input device. Additionally, some other embodimentsprovide an input device integrated with a display device that includes amodulated power supply to modulate signals provided to display elementsand touch sensing elements within the display and input devices.

FIG. 1 is a schematic block diagram of an input device 100, inaccordance with embodiments of the present technology. Although theillustrated embodiments of the present disclosure are shown as an inputdevice integrated with a display device, it is contemplated that theinvention may be embodied in the input devices that are not integratedwith display devices. The input device 100 may be configured to provideinput to an electronic system 150. As used in this document, the term“electronic system” (or “electronic device”) broadly refers to anysystem capable of electronically processing information. Somenon-limiting examples of electronic systems include personal computersof all sizes and shapes, such as desktop computers, laptop computers,netbook computers, tablets, web browsers, e-book readers, and personaldigital assistants (PDAs). Additional example electronic systems includecomposite input devices, such as physical keyboards that include inputdevice 100 and separate joysticks or key switches. Further exampleelectronic systems include peripherals such as data input devices(including remote controls and mice), and data output devices (includingdisplay screens and printers). Other examples include remote terminals,kiosks, and video game machines (e.g., video game consoles, portablegaming devices, and the like). Other examples include communicationdevices (including cellular phones, such as smart phones), and mediadevices (including recorders, editors, and players such as televisions,set-top boxes, music players, digital photo frames, and digitalcameras). Additionally, the electronic system could be a host or a slaveto the input device.

The input device 100 can be implemented as a physical part of theelectronic system, or can be physically separate from the electronicsystem. As appropriate, the input device 100 may communicate with partsof the electronic system using any one or more of the following: buses,networks, and other wired or wireless interconnections. Examples includeI²C, SPI, PS/2, Universal Serial Bus (USB), Bluetooth, RF, and IRDA.

In FIG. 1, the input device 100 is shown as a proximity sensor device(also often referred to as a “touchpad” or a “touch sensor device”)configured to sense input provided by one or more input objects 140 in asensing region 170. Example input objects include fingers and styli, asshown in FIG. 1.

Sensing region 170 encompasses any space above, around, in and/or nearthe input device 100 in which the input device 100 is able to detectuser input (e.g., user input provided by one or more input objects 140).The sizes, shapes, and locations of particular sensing regions may varywidely from embodiment to embodiment. In some embodiments, the sensingregion 170 extends from a surface of the input device 100 in one or moredirections into space until signal-to-noise ratios prevent sufficientlyaccurate object detection. The distance to which this sensing region 170extends in a particular direction, in various embodiments, may be on theorder of less than a millimeter, millimeters, centimeters, or more, andmay vary significantly with the type of sensing technology used and theaccuracy desired. Thus, some embodiments sense input that comprises nocontact with any surfaces of the input device 100, contact with an inputsurface (e.g. a touch surface) of the input device 100, contact with aninput surface of the input device 100 coupled with some amount ofapplied force or pressure, and/or a combination thereof. In variousembodiments, input surfaces may be provided by surfaces of casingswithin which the sensor electrodes reside, by face sheets applied overthe sensor electrodes or any casings, etc. In some embodiments, thesensing region 170 has a rectangular shape when projected onto an inputsurface of the input device 100.

The input device 100 may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region 170.The input device 100 comprises a plurality of sensing elements 124 fordetecting user input. The sensing elements 124 include a plurality ofsensor electrodes 120. As several non-limiting examples, the inputdevice 100 may use capacitive, elastive, resistive, inductive, magneticacoustic, ultrasonic, and/or optical techniques.

Some implementations are configured to provide images that span one,two, three, or higher dimensional spaces. Some implementations areconfigured to provide projections of input along particular axes orplanes.

In some resistive implementations of the input device 100, a flexibleand conductive first layer is separated by one or more spacer elementsfrom a conductive second layer. During operation, one or more voltagegradients are created across the layers. Pressing the flexible firstlayer may deflect it sufficiently to create electrical contact betweenthe layers, resulting in voltage outputs reflective of the point(s) ofcontact between the layers. These voltage outputs may be used todetermine positional information.

In some inductive implementations of the input device 100, one or moresensing elements 124 pickup loop currents induced by a resonating coilor pair of coils. Some combination of the magnitude, phase, andfrequency of the currents may then be used to determine positionalinformation.

In some capacitive implementations of the input device 100, voltage orcurrent is applied to create an electric field. Nearby input objectscause changes in the electric field, and produce detectable changes incapacitive coupling that may be detected as changes in voltage, current,or the like.

Some capacitive implementations utilize arrays or other regular orirregular patterns of capacitive sensing elements 124 to create electricfields. In some capacitive implementations, separate sensing elements124 may be ohmically shorted together to form larger sensor electrodes.Some capacitive implementations utilize resistive sheets, which may beuniformly resistive.

As discussed above, some capacitive implementations utilize “selfcapacitance” (or “absolute capacitance”) sensing methods based onchanges in the capacitive coupling between sensor electrodes 120 and aninput object. In various embodiments, an input object near the sensorelectrodes 120 alters the electric field near the sensor electrodes 120,thus changing the measured capacitive coupling. In one implementation,an absolute capacitance sensing method operates by modulating sensorelectrodes 120 with respect to a reference voltage (e.g. system ground),and by detecting the capacitive coupling between the sensor electrodes120 and input objects 140.

Additionally as discussed above, some capacitive implementations utilize“mutual capacitance” (or “transcapacitance”) sensing methods based onchanges in the capacitive coupling between sensor electrodes 120. Invarious embodiments, an input object 140 near the sensor electrodes 120alters the electric field between the sensor electrodes 120, thuschanging the measured capacitive coupling. In one implementation, atranscapacitive sensing method operates by detecting the capacitivecoupling between one or more transmitter sensor electrodes (also“transmitter electrodes”) and one or more receiver sensor electrodes(also “receiver electrodes”) as further described below. Transmittersensor electrodes may be modulated relative to a reference voltage(e.g., system ground) to transmit a modulated signals. Receiver sensorelectrodes may be held substantially constant relative to the referencevoltage to facilitate receipt of resulting signals. A resulting signalmay comprise effect(s) corresponding to one or more modulated signals,and/or to one or more sources of environmental interference (e.g. otherelectromagnetic signals). Sensor electrodes 120 may be dedicatedtransmitter electrodes or receiver electrodes, or may be configured toboth transmit and receive.

In FIG. 1, the processing system 110 is shown as part of the inputdevice 100. The processing system 110 is configured to operate thehardware of the input device 100 to detect input in the sensing region170. The processing system 110 comprises parts of or all of one or moreintegrated circuits (ICs) and/or other circuitry components. (Forexample, a processing system for a mutual capacitance sensor device maycomprise transmitter circuitry configured to transmit signals withtransmitter sensor electrodes, and/or receiver circuitry configured toreceive signals with receiver sensor electrodes). In some embodiments,the processing system 110 also comprises electronically-readableinstructions, such as firmware code, software code, and/or the like. Insome embodiments, components composing the processing system 110 arelocated together, such as near sensing element(s) 124 of the inputdevice 100. In other embodiments, components of processing system 110are physically separate with one or more components close to sensingelement(s) 124 of input device 100, and one or more componentselsewhere. For example, the input device 100 may be a peripheral coupledto a desktop computer, and the processing system 110 may comprisesoftware configured to run on a central processing unit of the desktopcomputer and one or more ICs (perhaps with associated firmware) separatefrom the central processing unit. As another example, the input device100 may be physically integrated in a phone, and the processing system110 may comprise circuits and firmware that are part of a main processorof the phone. In some embodiments, the processing system 110 isdedicated to implementing the input device 100. In other embodiments,the processing system 110 also performs other functions, such asoperating display screens, driving haptic actuators, etc. In one or moreembodiments, a grid electrode may be disposed between two or more sensorelectrodes 120 and processing system 110 may be configured to drive theguard electrode with a guarding signal which may be configured to guardthe sensor electrodes. In one embodiment, the guarding signal may be ashielding signal that is configured to guard and shield the sensorelectrodes. The grid electrode may be disposed on the same layer as thesensor electrode and comprise one or more common electrodes. In otherembodiments, the grid electrode may be disposed on a layer separate fromthe sensor electrodes. In on embodiment, a first grid electrode may bedisposed on a first layer common with the sensor electrode a second gridelectrode may be disposed on a second layer that is between the sensorelectrodes and an input surface of the input device 100. In oneembodiment, the grid electrode may be segmented in to multiple segmentsthat may be driven individually by the processing system 110. In oneembodiment a first grid electrode is disposed such that it at leastpartially circumscribes a first subset of sensor electrodes and a secondgrid electrode is disposed such that it is at least partiallycircumscribes a second subset of sensor electrodes. In otherembodiments, the input device 100 may comprise more than two gridelectrodes. In various embodiments, the grid electrode may be referredto as grid electrode. The grid electrode(s) and the sensor electrode mayencompass the entire surface of the V_(COM) electrode.

The processing system 110 may be implemented as a set of modules thathandle different functions of the processing system 110. Each module maycomprise circuitry that is a part of the processing system 110,firmware, software, or a combination thereof. In various embodiments,different combinations of modules may be used. Example modules includehardware operation modules for operating hardware such as sensorelectrodes and display screens, data processing modules for processingdata such as sensor signals and positional information, and reportingmodules for reporting information. Further example modules includesensor operation modules configured to operate sensing element(s) 124 todetect input, identification modules configured to identify gesturessuch as mode changing gestures, and mode changing modules for changingoperation modes.

In some embodiments, the processing system 110 responds to user input(or lack of user input) in the sensing region 170 directly by causingone or more actions. Example actions include changing operation modes,as well as GUI actions such as cursor movement, selection, menunavigation, and other functions. In some embodiments, the processingsystem 110 provides information about the input (or lack of input) tosome part of the electronic system (e.g. to a central processing systemof the electronic system that is separate from the processing system110, if such a separate central processing system exists). In someembodiments, some part of the electronic system processes informationreceived from the processing system 110 to act on user input, such as tofacilitate a full range of actions, including mode changing actions andGUI actions.

For example, in some embodiments, the processing system 110 operates thesensing element(s) 124 of the input device 100 to produce electricalsignals indicative of input (or lack of input) in the sensing region170. The processing system 110 may perform any appropriate amount ofprocessing on the electrical signals in producing the informationprovided to the electronic system. For example, the processing system110 may digitize analog electrical signals obtained from the sensingelements 124. As another example, the processing system 110 may performfiltering or other signal conditioning. As yet another example, theprocessing system 110 may subtract or otherwise account for a baseline,such that the information reflects a difference between the electricalsignals and the baseline. As yet further examples, the processing system110 may determine positional information, recognize inputs as commands,recognize handwriting, and the like.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Exemplary “zero-dimensional” positional informationincludes near/far or contact/no contact information. Exemplary“one-dimensional” positional information includes positions along anaxis. Exemplary “two-dimensional” positional information includesmotions in a plane. Exemplary “three-dimensional” positional informationincludes instantaneous or average velocities in space. Further examplesinclude other representations of spatial information. Historical dataregarding one or more types of positional information may also bedetermined and/or stored, including, for example, historical data thattracks position, motion, or instantaneous velocity over time.

In some embodiments, the input device 100 is implemented with additionalinput components that are operated by the processing system 110 or bysome other processing system. These additional input components mayprovide redundant functionality for input in the sensing region 170, orsome other functionality. FIG. 1 shows buttons 130 near the sensingregion 170 that can be used to facilitate selection of items using theinput device 100. Other types of additional input components includesliders, balls, wheels, switches, and the like. Conversely, in someembodiments, the input device 100 may be implemented with no other inputcomponents.

In some embodiments, the input device 100 comprises a touch screeninterface, and the sensing region 170 overlaps at least part of anactive area of a display screen of the display device 160. For example,the input device 100 may comprise substantially transparent sensingelements 124 overlaying the display screen and provide a touch screeninterface for the associated electronic system. The display screen maybe any type of dynamic display capable of displaying a visual interfaceto a user, and may include any type of light emitting diode (LED),organic LED (OLED), cathode ray tube (CRT), liquid crystal display(LCD), plasma, electroluminescence (EL), or other display technology.The input device 100 and the display device 160 may share physicalelements. For example, some embodiments may utilize some of the sameelectrical components for displaying and sensing. As another example,the display device 160 may be operated in part or in total by theprocessing system 110.

It should be understood that while many embodiments of the presenttechnology are described in the context of a fully functioningapparatus, the mechanisms of the present technology are capable of beingdistributed as a program product (e.g., software) in a variety of forms.For example, the mechanisms of the present technology may be implementedand distributed as a software program on information bearing media thatare readable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, the embodiments ofthe present technology apply equally regardless of the particular typeof medium used to carry out the distribution. Examples ofnon-transitory, electronically readable media include various discs,memory sticks, memory cards, memory modules, and the like.Electronically readable media may be based on flash, optical, magnetic,holographic, or any other storage technology.

FIG. 2A shows a portion of an exemplary pattern 200 of sensing elements124 configured to sense in the sensing region 170 associated with thepattern 200, according to some embodiments. For clarity of illustrationand description, FIG. 2A shows the sensor electrodes 120 of the sensingelements 124 in a pattern of simple rectangles, and does not showvarious other components. The exemplary pattern 200 of sensing elements124 comprises an array of sensor electrodes 120 _(X,Y) (referredcollectively as sensor electrodes 120) arranged in X columns and Y rows,wherein X and Y are positive integers. It is contemplated that thepattern of sensing elements 124 comprises a plurality of sensorelectrodes 120 having other configurations, such as polar arrays,repeating patterns, non-repeating patterns, a single row or column, orother suitable arrangement. The sensor electrodes 120 are coupled to theprocessing system 110 and utilized to determine the presence (or lackthereof) of an input object 140 in the sensing region 170.

In a first mode of operation, the arrangement of sensor electrodes 120(120-1, 120-2, 120-3, . . . 120-n) may be utilized to detect thepresence of an input object via absolute sensing techniques. That is,processing system 110 is configured to drive each sensor electrode 120with a signal and receive a resulting signal comprising effectscorresponding to the modulated signal, which is utilized by theprocessing system 110 or other processor to determine the position ofthe input object.

The sensor electrodes 120 are typically ohmically isolated from eachother. That is, one or more insulators separate the sensor electrodes120 and prevent them from electrically shorting to each other. In someembodiments, the sensor electrodes 120 are separated by an insulativegap. The insulative gap separating the sensor electrodes 120 may befilled with an electrically insulating material, or may be an air gap.

In a second mode of operation, the sensor electrodes 120 (120-1, 120-2,120-3, . . . 120-n) may be utilized to detect the presence of an inputobject via profile sensing techniques. That is, processing system 110 isconfigured to drive the sensor electrodes 120 row-by-row and thencolumn-by-column, with modulated signals. The signals generated inresponse to driving the sensor electrodes 120 in this configurationprovide information related to the position of an input object 140within the sensing region.

In a third mode of operation, the sensor electrodes 120 may be splitinto groups of transmitter and receiver electrodes utilized to detectthe presence of an input object via transcapacitive sensing techniques.That is, processing system 110 may drive a first group of sensorelectrodes 120 with a modulated signal and receive resulting signalswith the second group of sensor electrodes 120, where a resulting signalcomprising effects corresponding to the modulated signal. The resultingsignal is utilized by the processing system 110 or other processor todetermine the position of the input object.

The input device 100 may be configured to operate in any one of themodes described above. The input device 100 may also be configured toswitch between any two or more of the modes described above.

Areas of localized capacitive coupling may be termed “capacitivepixels.” Capacitive pixels may be formed between an individual sensorelectrode 120 and ground in the first mode of operation, between groupsof sensor electrodes 120 and ground in the second mode of operation, andbetween groups of sensor electrodes 120 used as transmitter and receiverelectrode in the third mode of operation. The capacitive couplingchanges with the proximity and motion of input objects 140 in thesensing region 170 associated with the sensing elements 124, and thusmay be used as an indicator of the presence of the input object in thesensing region of the input device 100.

In some embodiments, the sensor electrodes 120 are “scanned” todetermine these capacitive couplings. That is, in one embodiment, one ormore of the sensor electrodes 120 are driven to transmit modulatedsignals. Transmitters may be operated such that one transmitterelectrode transmits at one time, or multiple transmitter electrodestransmit at the same time. Where multiple transmitter electrodestransmit simultaneously, the multiple transmitter electrodes maytransmit the same modulated signal and effectively produce aneffectively larger transmitter electrode. Alternatively, the multipletransmitter electrodes may transmit different modulated signals. Forexample, multiple transmitter electrodes may transmit differentmodulated signals according to one or more coding schemes that enabletheir combined effects on the resulting signals to be independentlydetermined.

The sensor electrodes 120 configured as receiver sensor electrodes maybe operated singly or multiply to acquire resulting signals. Theresulting signals may be used to determine measurements of thecapacitive couplings at the capacitive pixels.

In another embodiment, the sensor electrodes may be operated such thatmore than one sensor electrodes is driven and received with at a time,or sensor electrodes are driven and received with at the same time. Insuch embodiments, an absolute capacitive measurement may be obtainedfrom each of the one or more sensor electrodes 120 simultaneously.

In one embodiment each of the sensor electrodes 120 are simultaneouslydriven and received with, obtaining an absolute capacitive measurementsimultaneously from each of the sensor electrodes 120. In variousembodiments, processing system 110 may configured to selectively driveand receive with a portion of sensor electrodes 120. For example, thesensor electrodes may be selected based on, but not limited to, anapplication running on the host processor, a status of the input device,and an operating mode of the sensing device.

A set of measurements from the capacitive pixels form a “capacitiveimage” (also “capacitive frame”) representative of the capacitivecouplings at the pixels. Multiple capacitive images may be acquired overmultiple time periods, and differences between them used to deriveinformation about input in the sensing region. For example, successivecapacitive images acquired over successive periods of time can be usedto track the motion(s) of one or more input objects entering, exiting,and within the sensing region.

The background capacitance of the input device 100 is the capacitiveimage associated with no input object in the sensing region 170. Thebackground capacitance changes with the environment and operatingconditions, and may be estimated in various ways. For example, someembodiments take “baseline images” when no input object is determined tobe in the sensing region 170, and use those baseline images as estimatesof their background capacitances.

Capacitive images can be adjusted for the background capacitance of theinput device 100 for more efficient processing. Some embodimentsaccomplish this by “baselining” measurements of the capacitive couplingsat the capacitive pixels to produce a “baselined capacitive image.” Thatis, some embodiments compare the measurements forming a capacitanceimage with appropriate “baseline values” of a “baseline image”associated with those pixels, and determine changes from that baselineimage.

In some touch screen embodiments, one or more of the sensor electrodes120 comprise one or more common electrodes used in updating the displayof the display screen. In one or more embodiment, the common electrodescomprise one or more segments of a V_(COM) electrode, a source driveline, gate line, an anode electrode or cathode electrode, or any otherdisplay element. These common electrodes may be disposed on anappropriate display screen substrate. For example, the common electrodesmay be disposed on the a transparent substrate (a glass substrate, TFTglass, or any other transparent material) in some display screens (e.g.,In Plane Switching (IPS) or Plane to Line Switching (PLS) Organic LightEmitting Diode (OLED)), on the bottom of the color filter glass of somedisplay screens (e.g., Patterned Vertical Alignment (PVA) orMulti-domain Vertical Alignment (MVA)), over an emissive layer (OLED),etc. In such embodiments, the common electrode can also be referred toas a “combination electrode”, since it performs multiple functions. Invarious embodiments, each of the sensor electrodes 120 comprises one ormore common electrodes. In other embodiments, at least two sensorelectrodes 120 may share at least one common electrode.

In various touch screen embodiments, the “capacitive frame rate” (therate at which successive capacitive images are acquired) may be the sameor be different from that of the “display frame rate” (the rate at whichthe display image is updated, including refreshing the screen toredisplay the same image). In various embodiments, the capacitive framerate is an integer multiple of the display frame rate. In otherembodiments, the capacitive frame rate is a fractional multiple of thedisplay frame rate. In yet further embodiments, the capacitive framerate may be any fraction or integer of the display frame rate.

Continuing to refer to FIG. 2A, the processing system 110 coupled to thesensing electrodes 120 includes a sensor module 204 and optionally, adisplay driver module 208. The sensor module 204 includes circuitryconfigured to drive a modulated signal onto the sensing electrodes 120during periods in which input sensing is desired. The modulated signalis generally a modulated signal containing one or more bursts over aperiod of time allocated for input sensing. The modulated signal mayhave an amplitude, frequency and voltage which may be changed to obtainmore robust location information of the input object in the sensingregion 170. The sensor module 204 may be selectively coupled to one ormore of the sensor electrodes 120. For example, the sensor module 204may be coupled to selected portions of the sensor electrodes 120. Inanother example, the sensor module 204 may be coupled to a differentportion of the sensor electrodes 120. In yet another example, the sensormodule 204 may be coupled to all the sensor electrodes 120 and operatein either an absolute or transcapacitive sensing mode.

In one or more embodiments, capacitive sensing (or input sensing) anddisplay updating may occur during at least partially overlappingperiods. For example, as a common electrode is driven for displayupdating, the common electrode may also be driven for capacitivesensing. In another embodiment, capacitive sensing and display updatingmay occur during non-overlapping periods, also referred to asnon-display update periods. In various embodiments, the non-displayupdate periods may occur between display line update periods for twodisplay lines of a display frame and may be at least as long in time asthe display update period. In such embodiment, the non-display updateperiod may be referred to as a long horizontal blanking period, longh-blanking period or a distributed blanking period. In otherembodiments, the non-display update period may comprise horizontalblanking periods and vertical blanking periods. Processing system 110may be configured to drive sensor electrodes 120 for capacitive sensingduring any one or more of or any combination of the differentnon-display update times, or during a display update time.

The sensor module 204 also includes circuitry configured to receive aresulting signal with the sensor electrodes 120 comprising effectscorresponding to the modulated signal during periods in which inputsensing is desired. The sensor module 204 may determine a position ofthe input object 140 in the sensing region 170 or may provide a signalincluding information indicative of the resulting signal to anothermodule or processor, for example, a determination module or a processorof the electronic device 150 (i.e., a host processor), for determiningthe position of the input object 140 in the sensing region 170.

The display driver module 208 may be included in or separate from theprocessing system 110. The display driver module 208 includes circuitryconfigured to provide display image update information to the display ofthe display device 160 during non-sensing (e.g., display updating)periods or during sensing periods.

As discussed above, the sensor electrodes 120 of the sensing elements124 may be formed as discrete geometric forms, polygons, bars, pads,lines or other shape, which are ohmically isolated from one another. Thesensor electrodes 120 may be electrically coupled through circuitry toform electrodes of having larger plan area relative to a discrete one ofthe sensor electrodes 120. The sensor electrodes 120 may be fabricatedfrom opaque or non-opaque conductive materials. In embodiments whereinthe sensor electrodes 120 are utilized with a display device, it may bedesirable to utilize non-opaque conductive materials for the sensorelectrodes 120. In embodiments wherein the sensor electrodes 120 are notutilized with a display device, it may be desirable to utilize opaqueconductive materials having lower resistivity for the sensor electrodes120 to improve sensor performance. Materials suitable for fabricatingthe sensor electrodes 120 include ITO, aluminum, silver, copper, andconductive carbon materials, among others. The sensor electrodes 120 maybe formed as contiguous body of conductive material having little or noopen area (i.e., having a planar surface uninterrupted by holes), or mayalternatively be fabricated to form a body of material having openingsformed therethrough. For example, the sensor electrodes 120 may beformed of a mesh of conductive material, such as a plurality ofinterconnected thin metal wires. In one embodiment, at least one of thelength and width of the sensor electrodes 120 may be in a range of about1 to about 2 mm. In other embodiments, at least one of the length andwidth of the sensor electrodes may be less than about 1 mm or greaterthan about 2 mm. In other embodiment, the length and width may not besimilar, and one of the length and width may be in the range of about 1to about 2 mm. Further, on various embodiments, the sensor electrodes120 may comprise a center to center pitch in the range of about 4 toabout 5 mm; however, in other embodiments, the pitch may be less thanabout 4 mm or greater than about 5 mm.

Modulated Power Supply for Reduced Parasitic Capacitance

When the sensor electrodes 120 are being driven with modulated signalsfor capacitive sensing, the sensor electrodes 120 may experience effectsrelated to parasitic capacitance due to capacitive coupling between thesensor electrodes 120 and other nearby conductive components such asother sensor electrodes 120, as well as traces and other electrodes. Insome embodiments, this parasitic capacitance can reduce the ability todetect the presence of that input object through the use of capacitivesensing techniques.

To reduce the effects related to parasitic capacitance, the power supplythat provides power to the various components of the input device 100 isconfigured to generate modulated power supply signals and a modulatedground signal. The modulated power supply signals and modulated groundsignal cause the various components of the input device 100 describedabove that would normally be held at a substantially constant voltagewith respect to earth ground to instead be driven with a modulatedsignal with respect to earth ground. In other words, by powering theinput device 100 with a modulated power supply, various signals in theinput device 100 are modulated. The sensor electrodes 120 can then beoperated simply by maintaining the sensor electrodes 120 at a constantvoltage with respect to the modulated ground signal. Since the inputobject 140 is (generally) at earth ground, the voltage differentialbetween the sensor electrodes 120 and the input object 140 varies withtime. Further, by maintaining the sensor electrodes 120 at a constantvoltage with respect to the modulated ground signal, and thus othercomponents of the input device 100, parasitic capacitance experienced bythe sensor electrodes 120 is reduced. More specifically, parasiticcapacitance is reduced because the voltage of the sensor electrodes 120remains substantially constant with respect to other components of theinput device 100.

In various embodiments, input device 100 may comprise display device 160having an integrated input sensing device. As is described above, insuch embodiments, one or more display electrodes may be configured toperform both display updating and capacitive sensing. During displayupdate periods, an electrode in the V_(COM) layer (common electrode orV_(COM) electrode) forms the fixed electrode for the storage capacitorand liquid crystal material, with the charge stored between the V_(COM)electrode and the pixel electrode. The amount of charge stored betweenthe V_(COM) electrode and pixel electrode determine the transmission oflight. For an OLED, during display update periods an electrode in thecathode layer (common electrode or cathode electrode) forms the fixedelectrode for the storage capacitor, with the charge stored between thecathode layer and an anode layer. During an input sensing period, theone or more common electrodes corresponding to sensor electrodes 120 aredriven to a first voltage potential and the resulting charge that isrequired drive the sensor electrode(s) to the first voltage potential ismeasured by the sensor module 204. In various embodiments, the sensorelectrodes may be driven with a modulated voltage that transitions thesensor electrode(s) between a first voltage potential and a secondvoltage potential. In other embodiments, processing system 110 may beconfigured to drive a sensor electrode with a predetermined amount ofcharge and the corresponding voltage on the sensor electrode ismeasured. In any of the above embodiments, the signal driven onto thesensor electrode may be referred to as a modulated signal and the chargeor current that is measured may be referred to as resulting signals thatare received with the sensor electrode(s). The resulting signalcomprises both local parasitic capacitances between a sensor electrodeand proximate conductors and the capacitance between the sensorelectrode and the input object. In various embodiments, the capabilitiesof the sensor module 204 and the input device 100 may be improved byreducing the parasitic capacitances that are present in the resultingsignals.

FIG. 2B illustrates a plurality of the local parasitic capacitances forsensor electrode 120. In the illustrated embodiment, Csource representsthe parasitic capacitance between the sensor electrode and a sourceline, Cadj represents the parasitic capacitance between the sensorelectrode and adjacent (or proximate) sensor electrodes, Cpe representsthe parasitic capacitance between the sensor electrode and the pixelelectrode and Cgate represents the parasitic capacitance between thesensor electrode and a gate line. The parasitic capacitances illustratedin FIG. 2B may a subset of a larger number of parasitic capacitances.Further, in various embodiments, there may be parasitic capacitivecouplings between the sensor electrode and multiple gate lines, sourcelines, adjacent sensor electrodes and/or pixel electrodes.

In one embodiment, a parasitic capacitance may be substantially reducedor eliminated by driving a guarding signal onto a sensor electrode thatis near to a sensor electrode that is driven for capacitive sensingand/or onto an electrode that serves another purpose, such as displayupdating. The guarding signal may be configured such that relativevoltage between electrodes (i.e., gate line, source line, sensorelectrodes) is substantially constant. Therefore, to eliminate or reducethe parasitic capacitance between a sensor electrode driven with amodulated signal for capacitive sensing and nearby electrodes, thenearby electrodes are driven with a guarding signal that is similar tothe modulated signal in at least one of frequency, phase and/oramplitude. This guarding signal may be referred to herein as simply a“modulated signal.”

In one embodiment, to effectively guard is to electrically isolate anadjacent electrode (such as the pixel electrode or any other nearbyelectrode) from the processing system. The electrical isolation willmaintain the relative voltage between this isolated electrode and asensor electrode being driven for capacitive sensing unchanged. However,the isolated electrode will also have parasitic capacitance to otherelectrodes, which will cause the voltage on the isolated electrode tonot be different relative to the sensor electrode driven for capacitivesensing. These other electrodes may also be driven with a guardingsignal. In one embodiment the pixel electrodes are isolated when thegate line turns off the access transistor.

In other embodiments, nearby electrodes are driven with a guardingsignal, substantially reducing the parasitic capacitance between thesensor electrode driven for capacitive sensing and nearby electrodes. Inone embodiment, an amplitude of the guarding signal maybe larger orsmaller than the amplitude of the modulated signal.

Any practical form of modulation may be applied by a modulated powersupply. In some embodiments, the modulation applied by the modulatedpower supply is a sine wave having a frequency of between 100 kHz and500 kHz. In other embodiments, other waveforms and/or frequencies may beapplied. In some embodiments, the power supply comprises an isolatedpower supply. In other embodiments, the power supply comprises anon-isolated power supply.

One benefit of including the modulated power supply in input device 100is that because the sensor electrodes 120 are held at a constant voltagewith respect to the modulated ground signal, the circuitry for drivingthe sensor electrodes 120 can be fabricated with minimal complexity. Anexample of suitable circuitry is provided with respect to FIG. 6.

A further benefit of including the modulated power supply is that whenthe components of the input device 100 are modulated, power consumptionrelated to induced current drawn due to parasitic capacitance isreduced. Thus, the amount of power required to drive the sensorelectrodes 120 is reduced as compared with an input device 100 that doesnot include a modulated power supply.

A further benefit of including the modulated power supply in inputdevice 100 is realized in embodiments of the input device 100 thatinclude a display device. With many traditional touch/displayembodiments, touch sensing must be conducted at a time in which pixelsin the display are not being updated. Embodiments of the presentinvention comprising an input device 100 integrated with a displaydevice benefit from the inclusion of a modulated power supply because amodulated power supply helps to facilitate a touch and display timingscheme in which touch sensing and display updating are performed duringat least partially overlapping time periods. This overlapping timingscheme is also referred to as “overlap timing” herein. Overlap timing isdiscussed in more detail with respect to FIG. 4B. Embodiments thatinclude a display are now discussed is greater detail with respect toFIGS. 3-7B.

FIG. 3 is a cross-sectional partial schematic view of a liquid crystaldisplay cell 300. The display cell 300 includes a common voltage layer(V_(COM) layer) 302, a source line 304, a gate line 306, liquid crystalmaterial 308, a pixel electrode 310, and a pixel transistor 312 having asource 312 a, a gate 312 b, and a drain 312 c. Although display cell isdepicted as a liquid crystal display cell 300, it should be recognizedthat display cell 300 may a different type of display cell, such as, forexample, organic light-emitting-diodes (OLED).

The V_(COM) layer forms one electrode of a capacitor that includesliquid crystal material 308 as the dielectric. A pixel electrode 310forms the opposite electrode of the capacitor. Applying a voltage acrossliquid crystal material 308 causes the liquid crystal material 308 tochange optical properties, which allows more or less light emitted froma backlight to pass through the liquid crystal material 308. The voltagelevel across the liquid crystal material 308 determines the amount oflight that passes through the liquid crystal material 308.

Updating pixel values is thus generally accomplished by setting thepixel electrode 310 to a certain voltage with respect to the V_(COM)layer 302. V_(COM) is typically held at a level somewhere between systemground and system Vcc (i.e., the power supply voltage). Generally,V_(COM) is held in the middle of these two voltages. The purpose ofholding V_(COM) at an intermediate voltage, rather than at absoluteground or at Vcc is so that a voltage balancing scheme such as dotinversion can be used. Dot inversion is a scheme whereby liquid crystalmaterials 308 are alternately charged with positive and then negativevoltage, so that a single voltage direction is not always applied acrossthe liquid crystal materials 308. Because liquid crystal materials 308may experience fatigue if voltage in only a single direction isrepeatedly or constantly applied, the inversion schemes described abovehelp to reduce or eliminate this fatigue.

In addition to functioning as a reference voltage for updating pixelvalues, V_(COM) may also be operated as a sensor electrode 120 for touchsensing. In prior art input devices in which V_(COM) is operated as asensor electrode 120, pixel values are updated, and then touch sensingis conducted. In other words, typically, “overlap timing” is notperformed, as described in greater detail below with respect to FIG. 4A.However, as described with respect to FIG. 4B, embodiments of thepresent invention allow touch sensing and display updating to beperformed in overlapping time periods.

FIG. 4A illustrates a graph 400 depicting operation of a conventionalinput device with touch sensing and pixel updating occurringsimultaneously without a modulated power supply. As can be seen byV_(COM) graph 402, while the voltage for V_(COM) is varying over time,the voltage at the pixel electrode, indicated by pixel electrode graph404, stays constant. Because the voltage for V_(COM) is varying, thevoltage difference between the pixel electrode and the V_(COM) electrodevaries over time, which means that the desired voltage differentialacross the liquid crystal material 308 is not being applied. This graph400 illustrates the traditional reason why pixel updates and touchsensing cannot be performed at the same time. A different scheme,depicted in FIG. 4B, allows pixel updates and touch sensing to beperformed at the same time.

FIG. 4B illustrates a graph 450 depicting operation of an input devicewith touch sensing and pixel updating occurring simultaneously,utilizing a modulated power supply. As can be seen, both the graph forV_(COM) 452 and the graph for the pixel electrode 454 vary with time.Additionally, the voltage differential (indicated by ΔV) between thepixel electrode 454 and V_(COM) 452 remains substantially constant.

Because the voltage on V_(COM) varies over time, V_(COM) can be used todetect capacitive coupling between V_(COM) and an input object 140. Morespecifically, the varying voltage of V_(COM) with respect to an inputobject 140 will induce an amount of current flow in V_(COM) that can bemeasured. Although the voltage of the pixel electrode 454 is varyingover time with respect to earth ground, the voltage differential betweenthe pixel electrode 454 and V_(COM) 452 remains substantially constant.Thus, a constant voltage differential is applied across the liquidcrystal material 308, which means that the liquid crystal material 308is able to be adjusted to a desired transmittivity. Any voltagedifferential between the pixel electrode and V_(COM) may be selected. Aslong as this voltage differential remains substantially constant, adesired value is applied to the sub-pixel element.

As has been illustrated by FIGS. 4A-4B, to use V_(COM) electrode(s) (orV_(COM)) as a sensor electrode, V_(COM) is modulated. This means thattraditionally, updating the pixel values cannot be done at the same timethat the input object is sensed. However, by modulating the powersupply, V_(COM) is modulated with respect to earth ground, and is heldconstant with respect to the voltage applied to the pixel electrode 310,which is also modulated. Further, by modulating the power supply,conductive elements within display cell 300 are modulated as well, whichmeans that parasitic capacitance between V_(COM) and these conductiveelements is reduced as compared with an input device 100 that does notinclude a modulated power supply. Further, because V_(COM) is modulated,sub-pixel values can be updated at the same time that the input objectis sensed.

FIG. 5A is a schematic diagram of a display device 500 integrated withan input device and including a modulated power supply, according to anembodiment. As shown, the display device 500 includes display panel 502,gate driver 504, source driver/receiver module 506, modulated powersupply 508, and processing system 510. Processing system 510 includesvarious modules, such as sensor module 512, determination module 514,and display driver module 516. The display panel 502 includes sensorelectrodes 120 that comprise common voltage (V_(COM)) electrodes. Thedisplay panel also includes sub-pixel elements 520. The sub-pixelelements 520 include components for displaying colors in pixels. Thedisplay panel 502 also includes a backlight and other components thatare not shown.

Referring momentarily to FIG. 3, the sub-pixel elements 520 each includepixel transistors for driving pixel electrodes 310. As depicted in FIG.3, the pixel transistors include a gate 312 b, a source 312 a, and adrain 312 c. The gate 312 b is coupled to gate driver 504. The source312 a is coupled to source driver/receiver module 506. The drain 312 cis coupled to the pixel electrode 310. As described with respect to FIG.3, the sub-pixel elements 520 may have a construction based on adifferent technology than liquid crystal (such as OLED), in which casethe sub-pixel elements 520 would have appropriate components.

Referring back to FIG. 5A, processing system 510 generally includes thefunctionality of processing system 110 depicted in FIG. 2A. The gatedriver 504 and source driver/receiver module 506 generate signals todrive each of the sub-pixel elements 520 for display. More specifically,the gate driver 504 selects a row of sub-pixel elements 520 by providinga gate voltage to a particular row of sub-pixel elements 520. The sourcedriver/receiver module 506 provides source signals to the sub-pixelelements 520 that are to be updated. The source signals are voltagelevels chosen to apply a particular voltage differential across liquidcrystal material 308 in order to cause liquid crystal material 308 totransmit the desired amount of light from the backlight, in liquidcrystal display embodiments. In other display technology embodiments(such as organic light emitting diode (OLED), the source signalsfunction differently, in accord with the particular display technology.

The source driver/receiver module 506 also includes circuitry configuredto receive resulting signals from sensor electrodes 120. In someembodiments, the source driver/receiver module 506 includes multiplereceiver channels that are each configured to measure the change incapacitance between one or more sensor electrodes 120 and an inputdevice. In one embodiment, measuring the change in capacitance comprisesholding a sensor electrode 120 at a particular voltage with respect topanel ground 532 while measuring an amount of current required to holdthe sensor electrodes 120 at that voltage. An example of a receiverchannel is circuit 600 depicted and described with respect to FIG. 6.Each of the sensing channels may be selectively coupled to one or moresensor electrodes 120 with selection circuitry such as one or moremultiplexers.

The source driver/receiver module 506 may be embodied as one or moreintegrated circuit chips configured to perform both touch sensing anddisplay updating functionality. In some embodiments, at least a portionof the functionality of the source driver/receiver module 506 isperformed by the sensor module 512. In other embodiments, the sensormodule 512 directs the source driver/receiver module 506 to drive thesensor electrodes 120 with desired signals. Further, in variousembodiments, sensor module 512 receives and processes the measuredchanges in capacitance from the source driver/receiver module 506.

In some embodiments, processing system 510 is configured to cause powersupply 508 to select between providing either a modulated referencesignal or a non-modulated reference signal to source driver/receivermodule 506 and to gate driver 504, so that sub-pixel elements 520 may bedriven with either modulated or non-modulated signals. Morespecifically, the gate driver 504 receives a gate driver power supplyvoltage 534 that is either modulated or non-modulated depending on theselection of processing system 510. Similarly, the sourcedriver/receiver module 506 receives a source driver power supply voltage536 that is either modulated or non-modulated depending on the selectionof processing system 510. These two power supply voltages may bereferred to herein as “reference voltages” and, when modulated, as“modulated reference voltages.” Thus, the source signals, that is, thesignals provided to the source terminals 312 a of the sub-pixel elements520, and the gate signals, that is, the signals provided to the gateterminals 312 b of the sub-pixel elements 520, are modulated or notmodulated based on whether the processing system 510 causes the powersupply 508 to provide modulated or non-modulated signals.

Referring momentarily to FIG. 5B, FIG. 5B illustrates an example circuit550 for driving a gate line with a modulated signal, according to anembodiment. In the embodiment illustrated in FIG. 5B, the switch(transistor pair) determines if the voltage output to the gate line iseither the gate voltage low (vgl) or voltage gate high (vgh) supplyvoltages. When the output is high, the voltage comes from vgh which ismodulated, so the output is modulated. If the output is low, the voltagecomes from vgl, so the output is also modulated.

Referring back to FIG. 5A, processing system 510 is configured todetermine periods in which to drive sensor electrodes 120 and displayelectrodes (e.g., source electrodes and/or gate electrodes) together. Insome embodiments, driving the display electrodes and sensor electrodes120 together includes driving the display electrodes with display updatesignals and the sensor electrodes 120 with capacitive sensing signals atthe same time.

During periods in which the processing system 510 drives the sensorelectrodes 120 and display electrodes together, processing system 510drives the sub-pixel elements 520 with modulated display update signalsand also drives sensor electrodes 120 with modulated capacitive sensingsignals. In some embodiments, the modulation applied to both displayupdate signals and capacitive sensing signals comprise voltagevariations to the same degree, frequency, and/or phase. In someembodiments, the modulation is applied uniformly, and thus the voltagedifferential between the signals applied to the source 312 a of thepixel transistor 312 and the sensor electrode 120 remains constant. Inthese circumstances, sub-pixel values are updated while both the V_(COM)(i.e., the sensor electrodes 120), source lines, and gate lines aremodulated with respect to earth ground.

In addition to driving the sensor electrodes 120 and display electrodestogether, at various different times, the processing system 510 maydrive either display electrodes and not sensor electrodes 120, or sensorelectrodes 120 and not display electrodes. In time periods in which theprocessing system 510 drives display electrodes but not sensorelectrodes 120, processing system 510 may drive the display electrodeswith non-modulated signals. Since sensor electrodes 120 are not drivenwith modulated signals during these time periods, effects related toparasitic capacitances are generally not experienced, and therefore thedisplay electrodes are not driven with modulated signals for guarding.

In one example, the sensor module 512 is configured to drive sensorelectrodes 120 with capacitive sensing signals that are based on amodulated reference signal during a first time period. These capacitivesensing signals are configured to modulate sensor electrodes 120 so thatcapacitive sensing may be performed, as is described above. The displaydriver module 516 is also configured to drive display electrodes withmodulated display update signals based on the modulated reference signalfor display updating during the first time period. The display updatesignals are configured to cause voltage between the display electrodesand the sensor electrodes to remain substantially constant. Thus, in thefirst time period, in which both capacitive sensing and display updatingoccurs, the display update signals and the touch sensing signals areboth modulated, which reduces the effects of parasitic capacitance. Thefirst time period may include all or part of the display update timesdiscussed above with respect to FIG. 2A.

Additionally, in some embodiments, the sensor module 512 is configuredto drive the sensor electrodes 120 for capacitive sensing during asecond time period, during which no display updating occurs. In thesecond time period, the display electrodes may be caused to float byswitching off the associated pixel transistor. In such a situation,where the display electrodes are floating, due to capacitive effects,the voltage at the display electrodes generally follows the voltage ofthe sensor electrodes 120 and thus does not contribute to parasiticcapacitances described above. Thus, in the second time period, in whichcapacitive sensing occurs, but display updating does not occur, thedisplay electrodes are not driven with modulated signals. In otherembodiments, the display electrodes may be held at a constant voltage.The second time period may include all or part of the non-display updateperiods (also referred to as “display update times”) discussed abovewith respect to FIG. 2A.

Further, in some embodiments, the sensor module 512 is configured to notdrive the sensor electrodes 120 for capacitive sensing during a thirdtime period, during which the display driver module 516 drives displayelectrodes for display updating. During the third time period, thedisplay driver module 516 drives the display electrodes withnon-modulated display signals. In the third time period, because thesensor electrodes are not driven for capacitive sensing, the parasiticcapacitance effects described above generally do not affect capacitivesensing, and thus the display electrodes are not driven with modulatedsignals. The third time period may include all or part of the displayupdate time discussed above with respect to FIG. 2A. In variousembodiments, any combination of the first, second, and third timeperiods may occur. For example, the first and second time periods mayoccur, the first and third time periods may occur, the second or thirdtime periods may occur, or other combinations of such time periods.

The processing system 510 also includes a determination module 514including determination circuitry configured to process signals receivedfrom source driver/receiver module 506. In some embodiments, theprocessing system 510 is configured to determine changes in capacitivecoupling between the sensor electrodes 120 and input object 140. Thedetermination module 514 may be selectively coupled to each of thereceiver channels in source driver/receiver module 506.

The display driver module 516 may be included in or separate from theprocessing system 510. The display driver module 516 includes circuitryconfigured to provide display image update information to the display ofthe display panel 502. More specifically, the display driver module 516includes circuitry for controlling gate driver 504 and sourcedriver/receiver module 506 to update sub-pixel elements 520 to specifiedvalues.

In one embodiment, the input device 100 comprises at least onecapacitive sensing controller coupled with modulated power supply 508.The capacitive sensing controller may be configured to provide themodulated power supply 508 with a modulated reference signal such thatthe modulated power supply 508 is configured to provide the modulatedsignals to the various display electrodes and the sensor electrodes. Inone embodiment, the modulated power supply 508 is configured to providemodulated reference signals to the gate lines, source lines and orcommon electrodes. In another embodiment, input comprises a timingcontroller coupled with a modulated power supply 508, wherein the timingcontroller is configured to provide the modulated power supply 508 withthe modulated reference signal.

When V_(COM) is modulated, V_(COM) can be used to detect the presence ofan input object through capacitive coupling. As the voltage at V_(COM)changes because of the modulation, a signal is generated that isindicative of an amount of capacitive coupling between the sensorelectrode 120 and an input object 140. An example circuit 600 formeasuring the capacitive coupling in this manner is provided below withrespect to FIG. 6.

FIG. 6 illustrates an example analog front end channel 600, alsoreferred to herein as an “AFE channel” for driving the sensor electrode120 for capacitive touch sensing. As shown, the AFE channel 600 includesa charge accumulator 602, a modulated power supply 508, a voltagedivider 610, and sensor electrode 120. It should be recognized thatwhile the modulated power supply 508 depicted in FIG. 6 is part of anelectric circuit with the AFE channel 600 and is thus electricallycoupled to the other components depicted in FIG. 6, the modulated powersupply 508 represents modulated power supply 508 depicted in FIG. 5A.Therefore, modulated power supply 508 depicted in FIG. 6 may be locatedin a different physical location from the rest of AFE channel 600.Additionally, it should be understood that while the sensor electrode120 is electrically coupled to the AFE channel 600 as shown in FIG. 6,the sensor electrodes 120 are not physically located within AFE channel600.

The AFE channel 600 includes a charge accumulator 602 for determining anamount of charge required to hold the sensor electrode at a constantvoltage with respect to a modulated ground signal. The chargeaccumulator 602 includes an operational amplifier 604 with capacitivefeedback between the inverting input and the output of the operationalamplifier. The non-inverting input is coupled to a reference voltagethat is modulated. In one embodiment, the modulated reference voltage isthe output of voltage divider 610, which maintains the modulatedreference voltage at a fixed voltage between the voltage of modulatedground and modulated power supply voltage. The positive voltage powersupply terminal and negative voltage power supply terminals of theoperational amplifier are coupled to the modulated power supply line 530and the modulated ground line 532 of the display panel 502,respectively.

As the modulated power supply voltage, modulated ground voltage, andmodulated reference voltage change due to the modulation, the output ofthe operational amplifier adjusts accordingly. More specifically, theoperation amplifier is configured such that the inverting input of theoperational amplifier follows the modulation signal applied to thenon-inverting input of the operational amplifier. Thus, the invertinginput of the operational amplifier, which is coupled to the sensorelectrode 120, causes the sensor electrode 120 to follow the modulationsignal. The voltage at the output of the operational amplifier indicatesan amount of charge required to hold sensor electrode 120 at a constantvoltage with respect to the modulated ground signal 612.

The charge accumulator 602 operates to maintain the sensor electrode 120at a constant voltage with respect to the modulated ground signal,although at a modulating voltage with respect to an input object 140.When an input object 140 is brought into the sensing region 170 near thesensor electrode 120, the amount of current that the operationalamplifier is required to flow in order to cause the voltage of thesensor electrode 120 to track the modulation changes as compared with astate in which no input object 140 is present in the sensing region 170.This amount of current flow is thus indicative of capacitive couplingbetween the sensor electrode 120 and the input object 140 and isreflected in the output of the operational amplifier.

The output of the charge accumulator 602 may be coupled to varioussupporting components such as demodulator circuitry, a low pass filter,sample and hold circuitry, other useful electronic components, such asfilters and analog-to-digital converters (ADCs) or the like. Thesupporting components function to take measurements from the chargeaccumulator 602 related to the capacitive coupling, or lack thereof, ofthe sensor electrode 120 to an input object 140.

Parasitic capacitance 620 is not a discrete element, but insteadrepresents an amount of capacitance between the sensor electrode 120 andother components in input device 100. Modulating the power supplyreduces the amount of parasitic capacitance as compared with an inputdevice that does not include a modulated power supply.

FIGS. 7A and 7B illustrate several display panel configurations thatillustrate different layouts for routing traces to the sensor electrode120 and sub-pixel elements 520. FIG. 7A illustrates a configuration thatincludes a single gate line. FIG. 7B illustrates a configuration thatincludes a dual gate line.

FIG. 7A is a close-up top-down view of a portion of display panel 502depicting a configuration 700 of touch and display elements. Theconfiguration 700 includes sensor electrodes 120 and sub-pixel elements520.

Each of the sensor electrodes 120 comprises a portion of a segmentedV_(COM) layer. Each sensor electrode 120 is roughly rectangular inshape, as shown. Additionally, each sensor electrode 120 overlaps foursub-pixel elements 520. In various embodiments, the sensor electrodes120 may overlap more or fewer than four sub-pixel elements 520. Thesensor electrodes 120 are ohmically isolated from each other, so thateach sensor electrode 120 can be driven separately. Although depictedwith a specific shape in FIG. 7A, the sensor electrodes 120 may beformed in any feasible shape, as those of ordinary skill in the artwould understand.

Sub-pixel elements 520 include a pixel electrode 310. Liquid crystalmaterial, not shown in FIG. 7A, is disposed between the pixel electrode310 and the sensor electrode 120. The pixel electrode 310 and sensorelectrode 120 work together to provide a voltage across the liquidcrystal material, as described with respect to FIG. 3.

Each of the sub-pixel elements 520 includes a pixel transistor 312having a gate 312 b, a source 312 a, and a drain 312 c. Gate lines 702couple the gates 312 b of the pixel transistors 312 to gate driver 504.Similarly, source lines 704 couple the sources 312 a of the pixeltransistors 312 to source driver/receiver module 506. Sensor electrodeline 706, which is coupled to sensor electrode 120 through connectionelement 705, and is disposed adjacent to source line 704, providessignals to the sensor electrode 120, and is coupled to sourcedriver/receiver module 506.

When a gate line 702 is activated, a signal provided over a source line704 is driven through the pixel transistor 312 activated by the gateline 702 to the pixel electrode 310 for the sub-pixel element 520 commonto both the driven gate line 702 and the driven source line 704. At thesame time, the sensor electrode 120, acting as a V_(COM) electrode, isheld at a constant voltage with respect to panel ground 532. The sensorelectrode 120 is coupled to an AFE channel, such as AFE channel 600, insource driver/receiver module 506, which determines an amount of currentrequired to hold the sensor electrode 120 at the constant voltage. Thus,pixel updating and touch sensing are performed at the same time.

FIG. 7B is a close-up top-down view of a portion of display panel 502depicting a configuration 750 of touch and display elements. As shown,the configuration 750 depicts sensor electrodes 120 and sub-pixelelements 520.

The sensor electrodes 120 and sub-pixel elements 520 are similar tothose depicted in FIG. 7A. However, each row of sub-pixel elementsincludes a first gate line 752 a and a second gate line 725 b instead ofjust a single gate line 702 as in FIG. 7A. The sub-pixel elements 520are alternatively coupled to the first gate line 752 a and the secondgate line 752 b. The use of two gate lines frees up space for the sensorelectrode line 756. This is because each of the source lines 754 can beused for two adjacent sub-pixels, which are selected by two differentgate lines 752 a and 752 b.

In addition to the configurations depicted in FIG. 7A and FIG. 7B,configurations in which the sensor electrode lines are disposed above orbelow the source lines or drain lines are possible as well. Morespecifically, the sensor electrode lines may be disposed directly aboveor below either the gate line or the source line, instead of beingadjacent to either of those lines.

CONCLUSION

Various embodiments of the present technology provide input devices andmethods for reducing parasitic capacitance in a capacitive sensing inputdevice. Particularly, embodiments described herein advantageouslyutilize a modulated power supply to modulate signals within an inputdevice to reduce the parasitic capacitances experienced by sensorelectrodes in the input device. Additionally, some other embodimentsprovide a display device with touch sensing capabilities that includes amodulated power supply to modulate signals provided to display elementsand touch sensing elements within the display device. With a modulatedpower supply, capacitive coupling between sensor electrodes and othercomponents of the input device is reduced, thereby increasing theability to sense input objects.

Thus, the embodiments and examples set forth herein were presented inorder to best explain the embodiments in accordance with the presenttechnology and its particular application and to thereby enable thoseskilled in the art to make and use the invention. However, those skilledin the art will recognize that the foregoing description and exampleshave been presented for the purposes of illustration and example only.The description as set forth is not intended to be exhaustive or tolimit the invention to the precise form disclosed.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

What we claim is:
 1. A processing system comprising: sensor circuitryconfigured to drive a first sensor electrode of a plurality of sensorelectrodes with a modulated capacitive sensing signal that is based on amodulated reference signal for capacitive sensing during a first timeperiod; wherein during the first time period a plurality of displayelectrodes of a display device is driven with modulated signals based onthe modulated reference signal.
 2. The processing system of claim 1,wherein the plurality of display electrodes and the at least one sensorelectrode have a substantially constant voltage differential during thefirst time period.
 3. The processing system of claim 1, wherein drivingthe plurality of display electrodes during the first time period withmodulated signals based on the modulated reference signal updates adisplay of the display device.
 4. The processing system of claim 1,wherein the plurality of display electrodes are driven withsubstantially non-modulated signals for updating a display of thedisplay device during a second time period, wherein the first timeperiod and the second time period are non-overlapping.
 5. The processingsystem of claim 1, wherein the sensor circuitry is further configured toreceive a resulting signal with a second sensor electrode of theplurality of sensor electrodes, the resulting signal comprising effectscorresponding to the modulated capacitive sensing signal.
 6. Theprocessing system of claim 1, wherein the sensor circuitry is furtherconfigured to receive a resulting signal with the first sensorelectrode, the resulting signal comprising effects corresponding themodulated capacitive sensing signal.
 7. The processing system of claim1, wherein: each of the plurality of sensor electrodes comprises atleast one common electrode of the display device and wherein theplurality of display electrodes comprises at least one of a plurality ofsource electrodes and a plurality of gate electrodes.
 8. The processingsystem of claim 1, wherein the modulated signals are at least one ofmodulated gate select signals and modulated source line update signals.9. The processing system of claim 1, wherein the modulated referencesignal is generated by a modulated power supply.
 10. The processingsystem of claim 1, further comprising display driver circuitryconfigured to drive the plurality of display electrodes of the displaydevice with the modulated signals based on the modulated referencesignal during the first time period.
 11. The processing system of claim1, wherein the first time period occurs between display line updateperiods of a display frame and wherein the first time period is at leastas long as a display line update period of the display frame.
 12. Aninput device comprising: a plurality of sensor electrodes; a pluralityof display electrodes; a modulated power supply configured to provide amodulated reference signal; and a processing system configured to: drivea plurality of sensor electrodes with modulated capacitive sensingsignals that are based on the modulated reference signal for capacitivesensing during a first time period; and drive a plurality of displayelectrodes of a display device with modulated signals based on themodulated reference signal during the first time period.
 13. The inputdevice of claim 12, wherein the plurality of display electrodes and theplurality of sensor electrodes have a substantially constant voltagedifferential during the first time period.
 14. The input device of claim12, further comprising a second plurality of sensor electrodes, whereinthe processing system is configured to receive resulting signals withthe second plurality of sensor electrodes during the first time period,the resulting signals comprising effects corresponding to the modulatedcapacitive sensing signals and to determine changes in capacitancebetween at least one sensor electrode of the plurality of sensorelectrodes and at least one sensor electrode of the second plurality ofsensor electrodes based on the resulting signals.
 15. The input deviceof claim 12, wherein the processing system is configured to: receiveresulting signals with the plurality of sensor electrodes, the resultingsignals comprising effects corresponding to the modulated capacitivesensing signals; and determine changes in capacitance between at leastone sensor electrode of the plurality of sensor electrodes and an inputdevice based on the resulting signals.
 16. The input device of claim 12,wherein the processing system is configured to update a display of thedisplay device by driving the plurality of display electrodes with themodulated signals during the first time period.
 17. The input device ofclaim 12, wherein the processing system is configured to drive theplurality of display electrodes with substantially non-modulated signalsfor display updating during a second time period, wherein the first timeperiod and the second time period are non-overlapping.
 18. The inputdevice of claim 12, wherein: each of the plurality of sensor electrodescomprises at least one common electrode of the display device.
 19. Amethod for operating an input device, comprising: driving a first sensorelectrode of a plurality of sensor electrodes with a modulatedcapacitive sensing signal that is based on a modulated reference signalfor capacitive sensing during a first time period, wherein during thefirst time period a plurality of display electrodes of a display deviceis driven with modulated signals based on the modulated referencesignal, and wherein the plurality of display electrodes and theplurality of sensor electrodes have a substantially constant voltagedifferential during the first time period.
 20. The method of claim 19further comprising receiving a resulting signal with a second sensorelectrode of the plurality of sensor electrodes, the resulting signalcomprising effects corresponding to the modulated capacitive sensingsignal.
 21. The method of claim 19 further comprising receiving aresulting signal with the first sensor electrode, the resulting signalcomprising effects corresponding to the modulated capacitive sensingsignal.